Bus Topology

In Bus Topology a cable is used to connect computers to the network. It is the co-axial cable which is used in this kind of topolgy. T-connectors are used to connect the computer to the cable. No much electronics is needed in this topology. Ends of the cable is terminated by the resistor.

Any computer whichever wants to send some data packet, send the packet on to the cable and packet is received by all the machines which are connected to the cable. But only that machine whose address matches with the destination address came along the packet accepts that packet.

What is this address and who places it in the Packet?

When you want to send some letter to some one you write the 'To' and 'From' address. Similrly when a packet of data is sent out by a computer on the network it places the address of the destination machine and it's own address in the packet. A computer network which follows TCP/IP standard to send and receive the data packets uses two different addresses which are placed in the packet which is sent out on the network. One is IP (Internet Protocol) address placed by the Network Layer and other is the MAC (Media Access Control) address placed by the Data Link layer. IP address is the logical address and MAC is the physical address present in the Network Interface card.

Diagram of Bus Topology

When a packet sent by one computer reaches every computer on the network, each of the machines check it's MAC address with destination MAC address which has come along with the packet and if it matches then the packet is sent to the next layer that is the Network Layer. Here it checks whether it's IP address matches with the destination IP address came along with the packet and if so the machine understands that the packet is for it and it accepts. If any one or none of the address match, the packet is rejected by the machine. Thus only that machine accepts the packet whose physical as well as logical address has matched.

You can see in this Bus Topology animation that when the packet color is green that means the packet belongs to that machine and it accepts and all other machines rejects it.

Bus topology has the advantage of not requiring every computer up and running in order for the network to work. But in Bus Topology a single cable is dedicated to all the information traffic, performance can be slow at times.

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Image of Bus Toplogy is from Google Images